PIC16F631/677/685/687/689/690
FIGURE 11-13:
EXAMPLE OF PWM DIRECTION CHANGE AT NEAR 100% DUTY CYCLE
Forward Period
Reverse Period
t1
P1A
P1B
PW
P1C
P1D
PW
TON
External Switch C
External Switch D
TOFF
Potential
T = TOFF – TON
Shoot-Through Current
Note 1: All signals are shown as active-high.
2: TON is the turn on delay of power switch QC and its driver.
3: TOFF is the turn off delay of power switch QD and its driver.
11.4.3
START-UP CONSIDERATIONS
When any PWM mode is used, the application
hardware must use the proper external pull-up and/or
pull-down resistors on the PWM output pins.
Note:
When the microcontroller is released from
Reset, all of the I/O pins are in the
high-impedance state. The external cir-
cuits must keep the power switch devices
in the OFF state until the microcontroller
drives the I/O pins with the proper signal
levels or activates the PWM output(s).
The CCP1M<1:0> bits of the CCP1CON register allow
the user to choose whether the PWM output signals are
active-high or active-low for each pair of PWM output pins
(P1A/P1C and P1B/P1D). The PWM output polarities
must be selected before the PWM pin output drivers are
enabled. Changing the polarity configuration while the
PWM pin output drivers are enabled is not recommended
since it may result in damage to the application circuits.
The P1A, P1B, P1C and P1D output latches may not be
in the proper states when the PWM module is
initialized. Enabling the PWM pin output drivers at the
same time as the Enhanced PWM modes may cause
damage to the application circuit. The Enhanced PWM
modes must be enabled in the proper Output mode and
complete a full PWM cycle before enabling the PWM
pin output drivers. The completion of a full PWM cycle
is indicated by the TMR2IF bit of the PIR1 register
being set as the second PWM period begins.
DS41262D-page 140
© 2007 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
